Brain's Workbench
Disabling firewalld
You can’t really run the old iptables utilities alongside firewalld. They’re just not compatible. The best way to get around this is to disable firewalld entirely (no need to uninstall it unless you want to) , and reinstall the iptables utilities. Disabling firewalld can be done using these commands:
Stop firewalld:
systemctl stop firewalld
Disable firewalld so it won’t start on boot:
# Generated by iptables-save v1.3.5 on Tue Oct 28 23:57:58 2014 *filter :INPUT ACCEPT [2590:547311] :FORWARD ACCEPT [11426:731834] :OUTPUT ACCEPT [3989:328501] -A INPUT -i eth0 -j ACCEPT COMMIT # Completed on Tue Oct 28 23:57:58 2014 # Generated by iptables-save v1.3.5 on Tue Oct 28 23:57:58 2014 *mangle :PREROUTING ACCEPT [24964:3178001] :INPUT ACCEPT [9150:1450474] :FORWARD ACCEPT [11426:731834] :OUTPUT ACCEPT [4655:374193] :POSTROUTING ACCEPT [15415:1060335] COMMIT # Completed on Tue Oct 28 23:57:58 2014 # Generated by iptables-save v1.3.5 on Tue Oct 28 23:57:58 2014 *nat :PREROUTING ACCEPT [0:0] :OUTPUT ACCEPT [0:0] :POSTROUTING ACCEPT [0:0] -A PREROUTING -m state -i eth0 --state RELATED,ESTABLISHED -j ACCEPT -A PREROUTING -p tcp -m tcp -d 123.45.67.89 --dport 80 -j DNAT --to-destination 172.16.5.113 -A POSTROUTING -j MASQUERADE COMMIT # Completed on Tue Oct 28 23:57:58 2014
Flushing all iptables chain rules shell script
#!/bin/sh
echo "Stopping IPv4 firewall and allowing everyone..."
ipt="/sbin/iptables"
## Failsafe - die if /sbin/iptables not found
[ ! -x "$ipt" ] && { echo "$0: \"${ipt}\" command not found."; exit 1; }
$ipt -P INPUT ACCEPT
$ipt -P FORWARD ACCEPT
$ipt -P OUTPUT ACCEPT
$ipt -F
$ipt -X
$ipt -t nat -F
$ipt -t nat -X
$ipt -t mangle -F
$ipt -t mangle -X
$ipt -t raw -F
$ipt -t raw -X
Make sure you can execute the script using the chmod command:
I got 5 Public IPs. i’m Gonna configure them, so Postfix can use multiple interfaces/ips for outgoing smtp connections.
First we need creating Interface aliases for those 5 public IPs.
In my system, using centos:
# cd /etc/sysconfig/network-scripts/ # cp ifcfg-eth0 ifcfg-eth0:1
Edit ifcfg-eth0:1 # vi ifcfg-eth0\:1
DEVICE=eth0 <-- default device HWADDR=XX:XX:XX:XX:XX:XX ONBOOT=yes TYPE=Ethernet BOOTPROTO=none IPADDR=202.XXX.XX.2 <-- default eth0 IP address PREFIX=24 GATEWAY=202.XXX.XX.1 DNS1=202.XXX.XX.XX
Change DEVICE and IPADDR parameters
Disable FirewallD
To disable the FirewallD on your CentOS 7 system, follow these steps: Type the following command to stop the FirewallD service:
sudo systemctl stop firewalld
Disable the FirewallD service to start automatically on system boot:
sudo systemctl disable firewalld
Mask the FirewallD service to prevent it from being started by another services:
sudo systemctl mask --now firewalld
Install and Enable Iptables
Perform the following steps to install Iptables on a CentOS 7 system:
Run the following command to install the iptables-service package from the CentOS repositories:
Download and Install the Iptables Service
To begin your server’s transition, you need to download and install the iptables-service package from the CentOS repositories. Download and install the service files by typing:
sudo yum install iptables-services
This will download and install the systemd scripts used to manage the iptables service. It will also write some default iptables and ip6tables configuration files to the /etc/sysconfig directory.
Construct your Iptables Firewall Rules
Next, you need to construct your iptables firewall rules by modifying the /etc/sysconfig/iptables and /etc/sysconfig/ip6tables files. These files hold the rules that will be read and applied when we start the iptables service.
How you construct your firewall rules depends on whether the system-config-firewall process is installed and being used to manage these files. Check the top of the /etc/sysconfig/iptables file to see whether it recommends against manual editing or not:
sudo head -2 /etc/sysconfig/iptables
If the output looks like this, feel free to manually edit the /etc/sysconfig/iptables and /etc/sysconfig/ip6tables files to implement the policies for your iptables firewall:
output # sample configuration for iptables service # you can edit this manually or use system-config-firewall
Open and edit the files with sudo privileges to add your rules:
sudo nano /etc/sysconfig/iptables sudo nano /etc/sysconfig/ip6tables
After you’ve made your rules, you can test your IPv4 and IPv6 rules using these commands:
sudo sh -c 'iptables-restore -t < /etc/sysconfig/iptables' sudo sh -c 'ip6tables-restore -t < /etc/sysconfig/ip6tables'
If, on the other hand, the output from examining the /etc/sysconfig/iptables file looks like this, you should not manually edit the file:
Allow IP forwarding
(Note: if your testing this on the same box your doing this on it won’t work, you need at least 3 machines to test this out, virtual ones work nicely)
First we enable ipv4 forwarding or this will not work:
# echo "1" > /proc/sys/net/ipv4/ip_forward
XOR
# sysctl net.ipv4.ip_forward=1
next we add a filter that changes the packets destination ip and allows us to masquerade:
# iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j DNAT --to-destination 10.0.0.3:80 # iptables -t nat -A POSTROUTING -j MASQUERADE
The above filter gets added to iptables PREROUTING chain. The packets first go through the filters in the PREROUTING chain before iptables decides where they go. The above filter says all packets input into eth0 that use tcp protocol and have a destination port 80 will have their destination address changed to 1.2.3.4 port 80. The DNAT target in this case is responsible for changing the packets Destination IP address. Variations of this might include mapping to a different port on the same machine or perhaps to another interface all together, that is how one could implement a simple stateful vlan (in theory).
Dynamic ports cannot be protected by port filtering firewalls such as iptables. First, you need to configure NFS services to use fixed ports. Open /etc/sysconfig/nfs, enter:
# vi /etc/sysconfig/nfs
Modify config directive as follows to set TCP/UDP unused ports:
# TCP port rpc.lockd should listen on. LOCKD_TCPPORT=lockd-port-number # UDP port rpc.lockd should listen on. LOCKD_UDPPORT=lockd-port-number # Port rpc.mountd should listen on. MOUNTD_PORT=mountd-port-number # Port rquotad should listen on. RQUOTAD_PORT=rquotad-port-number # Port rpc.statd should listen on. STATD_PORT=statd-port-number # Outgoing port statd should used. The default is port is random STATD_OUTGOING_PORT=statd-outgoing-port-number
1:1 NAT maps a single Public IP Address to one of your computer within your local area network (LAN). Unlike port forwarding, 1:1 NAT forwards all ports from one external IP to one internal IP.
iptables -t nat -A POSTROUTING -o eth0 -s 192.168.1.2 -j SNAT --to-source 83.229.64.2 iptables -t nat -A PREROUTING -i eth0 -d 83.229.64.2 -j DNAT --to-destination 192.168.1.2 iptables -A FORWARD -s 83.229.64.2 -j ACCEPT iptables -A FORWARD -d 192.168.1.2 -j ACCEPT
Port forwarding allows remote computers, for example, computers on the Internet, to connect to a specific computer or service within a private local area network (LAN).
Typical applications include the following:
In Linux, you can configure port forwarding using iptables command.
The below example is to enable the port forwarding of port 80 of the external ip address “83.229.64.2” to the port 80 of the computer inside the LAN with the ip address of “192.168.1.2”.
iptables -t nat -A PREROUTING -i eth0 -d 83.229.64.1 -p tcp --dport 80 -j DNAT --to-destination 192.168.1.2:80 iptables -A FORWARD -p tcp --dport 80 -j ACCEPT